There has been an increasing concern in recent years for improving the fuel economy performance of and for reducing the emission from internal combustion engines, particularly gasoline-fueled engines and diesel-fueled engines. Indeed, new engine oil specifications are requiring oil formulators to develop formulations containing less phosphorous while also reducing engine wear. Moreover, while the performance specifications have been increased, allowable treat rates for lubricant performance additives have been reduced.
Friction modifiers are typically used in engine oils to improve fuel efficiency. Such additives generally are either metal-containing compounds or ashless (non-metal-containing) organic compounds.
The trend toward low-ash lubricating compositions has focused oil formulators efforts on using ashless friction modifiers.
Ashless friction modifiers typically include fatty acid esters, fatty acid amides, organic dithiocarbamates or dithiophosphates.
In some instances, lubricant performance characteristics have been attained by a combination of specific lubricant additives that provide a synergistic result. For example, in US 2006/0189489 A1, the combination of glycerol monooleate and a nitrile compound purportedly shows synergistic friction reduction of a lubricating oil.